[chore][exporter/clickhouseexporter] Fix config comment (#31086)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
Just noticed the description for the `password` config option references
username instead of password.

exporter/clickhouseexporter/config.go

@@ -26,7 +26,7 @@ type Config struct {
 	Endpoint string `mapstructure:"endpoint"`
 	// Username is the authentication username.
 	Username string `mapstructure:"username"`
-	// Username is the authentication password.
+	// Password is the authentication password.
 	Password configopaque.String `mapstructure:"password"`
 	// Database is the database name to export.
 	Database string `mapstructure:"database"`